Viewed in the light of increasingly stringent requirements with respect to air pollution abatement, incineration of H.sub.2 S-containing off-gases is no longer a satisfactory means of disposal. Various procedures have been developed to remove the H.sub.2 S from the off-gases, and even recover, if possible, the H.sub.2 S or reaction products of H.sub.2 S. For example, the well-known Claus process produces an effluent normally containing up to 2 percent or even 3 percent by weight sulfur compounds, a substantial proportion being H.sub.2 S.
To remove this concentration of sulfur compounds, selective absorption and desorption of the Claus off-gases, after reduction, has been practiced. In this procedure, the bulk of the desorbed H.sub.2 S is returned to the Claus unit, and the final off-gas or tail gas, containing nitrogen, CO.sub.2 and quite minor amounts of H.sub.2 S is converted to SO.sub.2, a material which generally has not been subjected to emission requirements as rigid as those applied to H.sub.2 S. However, incineration is costly because of the necessary heat input. Again, although some work has been done with regard to catalytic conversion of the H.sub.2 S in the off-gas or tail gas to SO.sub.2, concomitant formation of SO.sub.3 has been a problem.
Andeeva, et al., Khim, Prom. (1946) No. 11, pp 17-18, also studied the oxidation of H.sub.2 S to SO.sub.2 in the presence and absence of catalysts. Among the catalysts studies were Ni, NiPb, NIBi, NiAg, NiMo, NiAl, NiPbAl, NiBiAl, and NiPbBi. According to the article, the most effective catalyst at 250.degree. to 300.degree. was NiAL, while the other catalysts required higher temperatures for equal results. The economic feasibility of this reported procedure is not known.
Accordingly, there has existed a need for an economical method for the removal of H.sub.2 S from H.sub.2 S-containing streams, particularly off-gas streams of the type mentioned, which method would provide substantial recovery of the H.sub.2 S values in the off-gas, and concomitantly provide low SO.sub.3 emissions. The present invention satisfies that need.